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Based on the force sensing quartz crystal EPKV-10M the several models of the balances are developed and made.

 

Prospective piezoresonance quartz pressure sensors

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  This article has been translated using google.translate service.

 Analyzing the current situation on the market of sensitive elements (SE) of the pressure sensors, the following basic principles of their action: piezoresistive, capacitive, piezoelectric and piezoresonance).

Piezoresistive pressure sensors with capacitive and SE are used widely, mode of operation and performance of these sensors can be found in many manufacturers, websites and in magazines.

Description of pressure sensors with piezoresonance sensors (PCHE) while less common, although this trend in Russia and abroad, developing intensively.

As such sensors PCHE used piezoelectric resonator of monocrystalline quartz, which is the electromechanical system using the phenomenon of direct and inverse piezoelectric effect,
uniting of the electrical excitation of mechanical vibration and removal of the electrical signal proportional to their amplitude [1, 2]. Quartz piezoelectric usually fixed at two points on the perimeter or siloperedayuschey membrane or beam. Under pressure membrane or beam deforms, respectively piezoelectric vibration frequency is proportional to the deformation. Figure 1 shows the structure model of quartz PCHE.

pic1 pic2pic3
а) b)          
Fig. 1 Models designs quartz PCHE:
a) high-frequency (HF) volume compression firm Quartzdyne (USA);
b) low frequency tuning fork membrane type company SKTB ELPA (Russia)                                                                       

 Using Quartz PCHE, the frequency of which varies under the influence of pressure on them, and foreign firms (such as: Quartzdyne, Spartek Systems, EpsonToyocom etc.) develop and produce a range of high-precision pressure sensors. Quartz pressure sensors have several advantages over capacitive sensors and piezoresistive sensitive element. These benefits are due, long-term stability of single-crystal quartz material of the PCHE sensors, a small change in the oscillation frequency PCHE at temperature over a wide range from -60 0 C to +150 0 C and the presence of the frequency output.

All of this gives:

 - High resolution (approximately 0.001% of full scale);

 - High precision measurement of pressure (on the order of 0.01% FS) in a wide temperature range, which is due to high Q, the choice of the cutting angle of monocrystalline quartz with low temperature dependence, the selection of connecting materials, structures fixing PCHE in the sensor housing, temperature compensation algorithm;

 - Long-term stability (about 0.01% FS per year)

 - Ability to work in a wide range of temperatures from cryogenic to 250 0C;

 - The ability to exclude from the measurement channel ADC, which is a source of additional error;

 - The ability to operate with a signal from a microprocessor.

 Besides quartz PCHE are resistant to radiation, which extends the range of applications.

 Sensors with quartz PCHE used as references in calibrators such firms as: Druc GE (UK); Ruska (U.S.); Artvik (U.S.); Fluke (USA), used in high precision barometer, also used to measure the hydrostatic pressure and the pressure in the oil and gas wells firms: Epson Toyocom (Japan); Aanderaa (Norway); Quartzdyne (U.S.); Schlumberger (France) and others,

 We should also note the SE with silicon resonators and pressure sensors based on these firm Yokogawa (Japan), which are also frequency and its characteristics are close to the quartz, but are limited by radiation resistance without special training.

 Russian companies are also developing and producing quartz manometer and thermosensitive PCHE-based construction for pressure and temperature, with technical characteristics similar to those foreign counterparts.

 The main developer and manufacturer of quartz PCHE in Russia is «SKTB ELPA", it produces two types of quartz manometric PCHE absolute pressure:

 1) membrane-type on a number of pressures from 0.0007 to 25 MPa, see Figure 1 (b) and Fig. 2;

 2) volume compression on a number of pressures from 0.02 to 150 MPa.

pic4 pic5
а) b)
Fig. 2 Quartz PCHE membrane type with Gage HF piezo                  

 They are used as a strain-sensing element double bass piezoelectric tuning fork for frequencies from 40 to 50 kHz and HF piezo stripe at a frequency of 10 MHz.
For reproducible elastic properties and the minimum reproducible temperature dependence of the connection to tenzochuvtvitelnye siloperedayuschey membrane or beam is in the evacuated housing PCHE performed as a single crystal quartz. All connections are made elements PCHE fusible glass with matched TCLE. The melting point of glass about 500 º C. The figure 2 a) shows the interconnected membrane liner and cover PCHE. The thickness of the connecting glass no more than 30 microns.
Temperature effect in manometric PCHE the operating temperature range, depending on the design can vary from 220 m to 1330 pF ppm, which is 0.5% and 3%, respectively, relative to the maximum frequency change in the operating pressure range.
Quartz pressure transducers to compensate for additional temperature error manometric PCHE used thermosensitive quartz resonators (RCT), the frequency of which varies depending on the temperature. On riunke 3 shows temperature-sensitive piezo with electrode system a) and a typical characteristic temperaturnochastotnaya (PMx) CT b). PMx described by a parabolic function with a theoretical point about extreme - 290 º C.

 

  pic6   graf1

     а)            б)
Fig. 3 temperature sensitive piezo                                                                   

Figure 4 shows the graphs clearly illustrate the characteristics of domestic quartz sensors with frequency and digital outputs.

graf2 graf3
                                                а)                                                                                  б)

graf4

c)
Figure 2 Characteristics of domestic quartz sensors with frequency and digital outputs:               
a) the resolution of + 0.002% for forward and backward movement of the sensor 60 cm . from the floor;
b) resistance to temperature changes when placed downhole sensor, with full scale of 80 MPa, the chamber 0 º C in liquid
thermostat to set it at 70 º C;
c) Long-term stability (total error barometric sensors installed on the ground in a street
During the year no more than ± 0.03% FS).

                                                                                           

But extensive use of domestic quartz PCHE in industry is limited by their dimensions, the lack (at the moment) quality oil-filled membrane separation unit, which allows their use in sensors for aggressive media and the complexity of the implementation based on these sensors and differential pressure.
We are working on the creation of a differential quartz PCHE, but for general use, it is also necessary to build a oil-filled membrane unit.
In addition, the task of miniaturization quartz PCHE and sensors. For example, to create a new quartz PCHE volumetric compression pressure from 0 to 60 MPa, the size of which 4h10h2 mm. and downhole pressure sensor based on it with dimensions Ø18 x 160 mm , Which is currently being tested.
Project developments underway PCHE other piezoelectric materials - langasite langatate and capable of operating at higher temperatures than quartz - up to 400 .. 500 º C.
Now there is a change of the old analog instrumentation for modern microprocessor-based devices, and quartz sensors, frequency and digital output should be more widely used.


REFERENCES

1. Малов В.В. Пьезорезонансные датчики. – 2-е изд., перераб. и доп. – М.:   Энергоатомиздат, 1989. 

2. Смагин А.Г., Ярославский М.И. Пьезоэлектричество кварца и кварцевые резонаторы. – М, Энергия, 1970.


The article was published in the journal "Компоненты и Технологии" №1 за 2011г.

Authors: Александр Поляков, Владимир Поляков, Михаил Одинцов.

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ВЫ НА СТРАНИЦЕ: Тех.поддержка Тех. поддержка Articles. Subject scope. Experiments. Prospective piezoresonance quartz pressure sensors
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